1. Field of the Invention
The present invention relates a method and an apparatus for manufacturing lens sheets such as Fresnel lens sheets.
2. Description of the Related Art
Japanese Laid-Open Patent Application Nos. S64-7001, S64-86102, H6-67002 and H7-148751 disclose a method for manufacturing various kinds of lens sheet such as Fresnel lens sheets, lenticular lens sheets or the like, which are to be used for a transmission type screen for a projection TV.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. S64-7001, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming die for Fresnel lens to form an uncured resin layer. Then, the ultraviolet ray curing type resin in the form of liquid is applied on the central portion of the uncured resin layer to form an uncured resin pool. Then, a sheet-shaped substrate is placed on the uncured resin pool. A surface plate is then placed on the substrate to press the uncured resin pool and the uncured resin layer together with the substrate against the forming die. Ultraviolet ray is irradiated on the ultraviolet ray curing type resin through the surface plate and the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming die, thus manufacturing a lens sheet.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. S64-86102, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming die to form an uncured resin layer. Then, the ultraviolet ray curing type resin in the form of liquid is applied on one side of the uncured resin layer to form an uncured resin pool. Then, a sheet-shaped substrate is placed on the uncured resin pool. The uncured resin pool and the uncured resin layer are pressed together with the substrate against the forming die by means of a pressing roller from the above-mentioned one side of the uncured resin layer toward the other side thereof so as to obtain a laminate structure of the substrate and the ultraviolet ray curing type resin, while excluding bubbles from the ultraviolet ray curing type resin. Then, ultraviolet ray is irradiated on the ultraviolet ray curing type resin through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming die, thus manufacturing a lens sheet.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. H6-67002, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming die to form an uncured resin layer. Ultraviolet ray is irradiated on the uncured resin layer to cure it. The ultraviolet ray curing type resin is applied on one side of the cured resin layer to form an uncured resin pool. Then, the uncured resin pool is spread through a sheet-shaped substrate into a uncured resin layer by means of a pressing roller so as to obtain a laminate structure of the substrate, the cured resin layer and the uncured resin layer, while excluding bubbles from the ultraviolet ray curing type resin. Then, the ultraviolet ray is irradiated on the uncured resin layer through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming die, thus manufacturing a lens sheet.
According to the manufacturing method, which is disclosed in Japanese Laid-Open Patent Application No. H7-148751, a lens sheet is manufactured by carrying out the following steps. First, ultraviolet ray curing type resin in the form of liquid is applied on the entirety of the upper surface of a forming die to form an uncured resin layer. Solvent contained in the ultraviolet ray curing type resin is vaporized by a hot-air dryer to form a solvent-vaporized layer. Then, the ultraviolet ray curing type resin is applied on one side of the solvent-vaporized layer to form an uncured resin pool. Then, the uncured resin pool is spread through a sheet-shaped substrate into a uncured resin layer by means of a pressing roller so as to obtain a laminate structure of the substrate, the solvent-vaporized layer and the uncured resin layer, while excluding bubbles from the ultraviolet ray curing type resin. Then, the ultraviolet ray is irradiated on the uncured resin layer through the substrate to cure it. Then, the cured resin is peeled together with the substrate from the forming die, thus manufacturing a lens sheet.
However, the above-mentioned prior art has a problem that a relatively large amount of bubbles is entrapped in the ionizing radiation curing type resin such as the ultraviolet ray curing type resin, which is applied on the forming die.